对于可重复读(repeatable read),查询只承认在事务启动前就已经commit的数据;
对于读提交(read committed),查询只承认在语句启动前就已经commit的数据;
SELECT @@tx_isolation;
SELECT @@global.tx_isolation;
https://stackoverflow.com/questions/41825832/mysql-how-to-find-out-isolation-level-for-the-transactions
SET SESSION TRANSACTION ISOLATION LEVEL READ COMMITTED;
SET SESSION TRANSACTION ISOLATION LEVEL REPEATABLE READ;